This invention relates to an iris diaphragm which is particularly, but not exclusively, for use with spot lights.
An iris diaphragm comprises a number of overlapping curved leaves mounted in a circle around an aperture, which can be rotated in unison to adjust the diameter of the aperture. Iris diaphragms are commonly used with spot lights, to narrow or broaden the beam of light. They are also used to regulate the amount of light entering an optical instrument, for example a camera.
An iris diaphragm comprises a base provided with an aperture, a rotatable element provided with a corresponding aperture, and a number of curved leaves, one end of which are mounted in a fixed pivotal position to one of the element or base, and the other end of which are mounted in a sliding pivotal position to the other of the element or base.
The leaves are mounted at equal points around the circumference of the aperture, and are so shaped that the curve along their inner edge corresponds to the curvature of the aperture, so when they are in the fully retracted position the aperture is unobstructed.
When the element or the base is rotated the leaves are rotated about their fixed pivot and cross over the aperture. Most irises can move from a fully open position to a fully closed position in approximately 110 degrees of rotation.
Spot lights are commonly cumbersome in size and shape, and can be fitted with adjustable colour filters and various electronic or electric components. The iris diaphragm is mounted before the light chamber, in the vicinity of any filters or the like.
An iris diaphragm comprising an aperture corresponding to the size of a spot light can be large in size. In particular, the base, rotating element, fixed and sliding pivots combine to produce an item which can be several centre meters in width. This can be a problem when several independent items of equipment have to be mounted before a spot light.
The present invention is intended to overcome some of the above problems.